Study: Newer COVID-19 Variants Have Shorter Incubation Periods

COVID-19 typically has an incubation period of two to 14 days before symptoms appear. But a new study published JAMA Network Open found that the incubation period for COVID-19 has gradually decreased as the virus evolved.

Researchers found that the Alpha variant had an average incubation period of five days, while the Omicron variant has an average of 3.42 days.

But there’s no guarantee that COVID-19 symptoms will show up even earlier with the next variants, said Egon Ozer, MD, PhD, an infectious diseases specialist at Northwestern Medicine.

The mechanism behind the shorter incubation period of Omicron variants is unclear. Ozer speculates that the increased binding capacity of the mutated spike protein in newer variants may result in more efficient infections with shorter incubations. The tendency of Omicron to infect upper airway cells rather than those lower in the lungs might also play a role, but these are just theories.

More research in the coming months will likely shed light on this matter, he added.

Why Is the Incubation Period Important?

Incubations periods give an idea of when people might become contagious if they were infected with COVID-19, said Mark Loafman, MD, MPH, a family physician and chair of the Family and Community Medicine Department at Cook County Health.

People who are infected may be infectious one or two days before symptom onset. Knowing the timeline can affect contact tracing, quarantine, and isolation recommendations, he added.

“A shorter incubation period can easily make a small local outbreak spread more quickly and widely, favoring that variant over others,” Loafman said.

Ozer explained that shorter incubation periods can reduce the time and uncertainty for people who need to test after having a known COVID-19 exposure. However, the milder symptoms associated with an Omicron infection are more likely to be dismissed as the common cold or allergies. This suggests that people should test more frequently to be safe, especially if they had known exposure.

Now that the updated bivalent COVID-19 boosters have been authorized, eligible individuals should get the shot to protect themselves against a potential surge this fall and winter.

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